Heat-sensitive diazotype material coated sheet



United States Patent 3,288,627 HEAT-SENSITTVE DIAZOTYPE MATERIAL COATEDSHEET Edward C. Bialczak, Mount Prospect, IlL, assignor toAdtiressograph-Multigraph Corporation, Cleveland, Ohio, a corporation ofDelaware No Drawing. Filed Aug. 5, 1965, Ser. No. 477,594 Claims. (Cl.11736.8)

This invention relates to heat-sensitive diazotype materials and toalkaline donor developers incorporated in such materials. Moreparticularly, it relates to metallic dialkyldithiocarbamate-aminecomplexes and heat-sensitive diazotype materials coated with suchcomplexes.

Heat-sensitive diazotype materials comprise a base member coated with aformulation containing a diazo compound and a coupling component withwhich the diazo compound reacts under proper conditions to form an azodye which produces a visible image. In making a print, the diazotypematerial is exposed to light under a translucent master. In those areasof the diazotype material which are exposed to light, thelight-sensitive diazo compound is at least partially destroyed, but isunaffected in the shaded areas. The print is then developed by heatingthe diazotype material and causing the alkaline donor developing agentto emit ammonia or an organic amine which produces the proper pHconditions for interaction of the diazo compound and the couplingcomponent. These react to produce a dye image in the shaded area whichcorresponds to the graphic material on the master.

In conventional heat-sensitive diazotype materials the alkaline donordeveloper is commonly a urea or thiourea compound which on decompositionat elevated temperatures yields ammonia which induces the couplingreaction to form the azo dye. Urea and thiourea compounds producediazotype materials having a relatively poor shelf life due toprecoupling of the diazo compound and the coupling component at ambienttemperatures. Other heat-sensitive diazotype materials which have longershelf lives usually require higher temperatures to induce coupling.Generally, these temperatures are too high for office equipment andoften they are so high that the diazo compound decomposes more rapidlythan it reacts with the coupling component to form the azo dye. To copewith the problem of precoupling, increased amounts of acid have beenused to stabilize the formulations, thus requiring increased amounts ofalkaline donor to be incorporated into the formula to provide asuflicient source of ammonia to give a suitably dense image. Forexample, British Patent No. 909,491 proposes the use of certain types ofacids which lose their acidity on heating and thereby reduce therequired quantity of alkaline donor since at developing temperatures theacid is dissipated.

It is an object of this invention to provide heat-sensitive diazotypematerials wherein the alkaline donor is stable at ambient temperature,decomposes to produce alkaline substances at relatively low temperatureand does not contribute to precoupling. It is another object of thisinvention to provide heat-sensitive diazotype materials which form goodprints and which have extended shelf life. It is a further object toprovide alkaline donor materials for heat-sensitive diazotype materialswhich decompose at relatively low temperatures to provide alkalinematerials which induce dye formation. These and other objects areapparent from and are achieved in accordance with the followingdisclosure.

In accordance with this invention it has been discovered that metallicdialkyldithiocarbamates form complexes with relatively strong organicamines. In these com- Patented Nov. 29, 1966 ICC plexes, which have thefollowing general formula, one

mole of metallic dialkyldithiocarbamate is combined with one mole ofamine:

Me--Am R RlNCSS wherein R R R and R are lower alkyl radicals, Me is ametal (zinc, cadmium or tellurium) and Am is an organic amine. Among thealkyl radicals which R R R and R represent are methyl, ethyl, propyl,butyl, isobutyl and amyl radicals.

The organic amine, Am, can be any of a wide variety of non-aromaticamines containing 4 to 10 carbon atoms, inclusive. Primary aliphaticamines such as methylamine, ethylamine, n-butylamine, t-butylamine,hexylamine and decylamine are operative. Secondary aliphatic amines suchas dimethylamine, methylethylamine, methyl-n-butylamine, anddi-n-butylamine are also included in this group. Tertiary aliphaticamines which are operative include trimethylamine, triethylamine and thelike.

The organic amine, Am, can also include alicyclic amines such ascyclohexylamine, N-methylcyclohexylamine, N-isopropylcyclohexylamine,N-butylcyclohexyL amine, N (2 cyanoethyl)cyclohexylamine,cyclobutylamine, N-methylcyclobutylamine, cyclopentylamine, N-ethylcyclopentylamine, :cycloheptylamine, cyclooctylamine and relatedamines.

Hydroxyamines such as N (2 hydroxyethyl)cyclohexylamine andN-(Z-hydroxypropyl)cyclohexylamine are useful in this invention, as arediamines such as N (2 aminoethyl)cyclohexylamine andN-(3-aminopropyl)cyclohexylamine. When diamines are combined with themetallic dialkyldithiocarbamate, they form complexes with both one moleand two moles of the metallic salts.

One important characteristic which determines the suitability of aparticular amine as an alkaline donor when combined as a complex with ametallic dialkyldithiocarbamate is the pH of the complex in 10% aqueousmixture. Suitable amines form complexes which produce pH values notgreater than 8.

The preferred amines in this invention are cyclohexylamine, t-butylamineand derivatives of cyclohexylamine such as N (2cyanoethyl)cyclohexylamine, N-(2- hydroxyethyl)cyclohexylarnine and Nisopropylcyclohexylamine.

The complexes are readily produced by treating a slurry of a metallicdialkyldithiocarbamate in an inert solvent, such as benzene or otherhydrocarbon liquid, with an equivalent quantity of the organic am ne inthe same solvent. The complex is insoluble in hydrocarbon solvents andcan be readily isolated by filtration.

The metallic dialkyldithiocarbamate-amine complexes are dispersed in aninert solvent, such as toluene, in any conventional dispersion mill andapplied directly to the substrate (e.g., paper) by roller coating orsimilar techniques in conjunction with an air knife or other suitabledoctoring means. The alkaline donor coating can be applied as a precoatto the photosensitive coating or it can be applied over an existingphotosensitive layer.

The metallic dialkyldithiocarbamate-amine complexes are water-insoluble,are stable at room temperature and dissociate in the temperature rangefrom to C., releasing the amine. The latter raises the pH of thediazotype material and creates an environment in which the diazocompound can react with the coupling component to form an azo dye.

The light-sensitive diazo compounds which are useful in two-componentdiazotype systems can also be used to a advantage in thermallyresponsive diazotype materials. Examples of such compounds are thediazonium salts ob tained by the diazotization of the following amines:

The preferred diazo compound is the zinc chloride double salt of4-morpholinobenzenediazonium chloride.

Generally, a number of coupling components may be employed. Thepreferred coupling component that may be employed to produce the dyeimage is 2,4-dihydroxynaphthalene-6-sulfonic acid. Other known couplersmay be employed such as resorcinol, acetoacetanilide, 4-chlororesorcinoland diacetoacetylethylenediamine. It is, of course, desirable to selectcoupling components which have little tendency to react with the diazocompounds until the alkaline donor developer has released the amine uponbeing heated above about 100 C.

To prevent precoupling and premature dye formation, there can be addedan acid component to keep the pH below the level required for coupling.Sulfonic acid derivatives, such as m-benzenedisulfonic acid, areemployed as the preferred acid components. Other acids may be used toproduce the desired pH such as:

oxalic acid citric acid tartaric acid lactic acid maleic acid malonicacid ethanesulfonic acid benzenesulfonic acid 'of diazo compound andcoupling component.

The complexes of this invention, when exposed to heat, undergodissociation to yield the corresponding amines which react with the freeacid in the diazotype formulation. It is seen that the alkaline donorsof this invention tend to lower the temperature to which the diazotypematerials are subjected, simplify the equipment, produce more intensecopy since the high temperatures which would degrade the diazo salts areavoided and increase the shelf life of diazotype materials.

When the metallic dialkyldithiocarbamate-amine complexes are applied tosheet materials in the production of diazotype materials, they aredispersed in fine particulate form in an organic solvent such as ahydrocarbon liquid (e.g., toluene) and the resulting suspension appliedto the sheet material by conventional coating procedures. The complexesare usually present in the suspensions or dispersions at concentrationsof 1% to 10% by weight, the range from 2% to 5% being preferred. Thedonor coating should be applied at a rate sufficient to afiord in therange of 0.075 to 0.250 gram of complex per square foot of substrate,the preferred concentration being in the range of 0.1 to 0.125 gram ofcomplex per square foot on a dry basis. After the solvent evaporates,the complexes form a thin coating of fine particles which can release anorganic amine when activated by heat. It was found that the alkalinedonor should be crystalline in form so that itmay be dispersed asparticulate material in a solvent vehicle and deposited on the substrateas distinct particles.

In the photosensitive coating formulations for sheet materials, theamount of diazo compound is usually convention. It generally constitutes2% to 6% of the formulation with 4% being preferred. Equivalentquantities of coupling reagent are employed, following conventionalpractice. The coating formulations are applied in amounts which willprovide about 15 grams of diazo compound for 3,000 square feet ofsurface on a dry basis.

The base or substrate for the diazotype material can be paper or anyother web or film material which is stable at 100150 C. Polyester filmssuch as sold under the trade names Mylar and Kodar are suitable filmmate- Example 1 Three moles of zinc dimethyldithiocarbamate (917 grams)are mixed with 5 liters of benzene. The mixture is stirred for severalhours forming a slurry. To the slurry there are gradually added 3 moles(297 grams) of cyclohexylarnine in 350 milliliters of benzene whichresult in the formation of the zincdimethyldithiocarbamatecyclohexylamine complex. The complex is filteredoff under suction and washed with lbetnzene to remove unreacted amine.The yield was of product 'having a melting point in the range of 153 to155 C. and a pH of a 10% complex-Water mixture of 8.0.

The complex obtained from the above procedure is used by applying it asa separate donor precoat to the base support for the thermal diazosheet. A typical donor coating formulation is as follows:

Parts by weight The amine metallic alkyl dithiocarbamate complex 2.5Toluene The complex is dispersed in the toluene by any conventionaldispersion type will equipment and applied directly to a paper substrateby the use of roller coating techniques in conjunction with an airknife.

On top of the donor coating there is applied photosensitive coating ofwhich the following is a typical formula:

Ingredient: Parts by weight Water 100 Citric acid 2 Thiourea 42,3-dihydroxynaphthalene-6-sulfonic acid 6 Zinc sulfate 4p-Diazo-N-ethyl-N-hydroxyethylaniline 1 Silica particles (finelydivided) 5 Rice starch 3 Polyvinyl acetate emulsion 8 This diazotypepaper is stable in storm has a long shelf life and can be developed atrelatively low temperature (HO- C.).

Example 2 Three moles of cadmium dibutyldi-thiocalibamate suspended in 5liters of toluene are treated with 3 moles ofN-(Z-hydroxyethyl)cyclohexylamine according to the procedure ofExample 1. The resulting complex is collected on a filter, washed withtoluene and dried. It is dispersed in toluene (5 parts in 100 parts oftoluene) and the dispersion is coated on a dry diazotype paper coatedwith the photosensitive coating shown in Example 1. The resulting diazotype paper is stable in storage and can be developed at 115130 C.

Example 3 Other metallic dialkyldithiocanba-mate-amine complexes whichare suitable in diazotype materials such as that described in Example 1are listed below. These are prepared by the method of Example 1 byreacting a mole of the metallic dialkyldithiocarbamate with a mole ofamine in an inert solvent such as benzene or toluene. In the case ofdiamines, two moles of the carbamate are reacted with one mole of thediamine. Each of these complexes dissociates at the temperature listedin (the table below under developing temperature and releases aminewhich induces coupling of the diazo compound and the coupling componentto form a dye which has the dye density listed in the table. In thetable the developing temperature is measured on a hotplate device andrepresents the temperature at which the amine is released.

Dye Devel- Density oping Temp, C.

Zinc dimethyldithiocarbamate cyclohexylamine." 1.1 115 Zincdiethyldithiocarbamate cyel0hexylamine .83 105 Zincdibutyldithiocarbamate cyclohexylamine 1. 1 115 Zincdiethyldithioearbamate tort-butylamine 1. 04 115 Zincdiethyldithiocarbamate N-(2-hydr0xyethyl) cyelohexylamine 1. 02 130 Zincdiethyldithiocarbamate N-(Z-cyanoethyl) cyclohexylamine 1. 30 138 Zincdiethyldithiocarbarnate N-isopropylcyclohexylarnine 87 138 Zincdimethyldithiocarbamate N-(Z-hydroxyethyl) cyelohexylamine 90 140 Zincdimethyldithiocarbamate tert-butylamine .90 145 Zincdimethyldithioearbamate N-(2-cyanoethy1) cyelohexylamine 90 152 Zincdibutyldithiocarbamate N-(Z-cyanoethyl) eyelohexylamine 73 125 Zincdimethyldithiocarbamate N-isopropylcyelohexylamine 85 145 Zincdimethyldithiocarbamate N -ethyleyclohexylamine 75 145 Zincdimethyldithiocarbamate N-(3-aminopropy1) cyelohexylamine 79 145 Dilzincdunethyldithiocarbamate] N-(3-aminopropyl) cyelohexylamine 82 145 Zincdibutyldithiocarbamate N-isopropyleyclohexyhmina 43 138 Cadmiumdiethyldithiocarbamate cyclohexylamine 8 105 Cadmiumdimethyldithioearbamate eyclohexylamin 1. O 125 Telluriumdiethyldithioearbamate eyelohexylamine 1. O4 115 I claim:

1. A heat-sensitive diazotyp'e material comprising a base sheet coatedwith a diaz-o compound, a coupling component and an alkaline donormetallic dialkyldithiocanbamate-amine complex, wherein the metal isselected from the group consisting of zinc, cadmium and telluriurn, thealkyl radicals contain 1 to 5 carbon atoms, inclusive, and the amine isselected from the gnoup consisting ctf aliphatic and alicyclicaminescontaining 4 to 10 carbon atoms, inclusive.

2. A heat-sensitive diazotyipe material comprising a base sheet coatedwith a diazo compound, a coupling component and an alkaline donormetallic dialkyldithiocarbamate-amine complex as defined by claim 1wherein the amine is an aliphatic amine containing 4 to 10 carbon atoms,inclusive.

3. A heat-sensitive diazotype material comprising a base sheet coatedwith a diazo compound, a coupling component and an alkaline donormetallic dialkyldithiocarbamate-amine complex as defined by claim 1wherein the amine is an alicyclic amine containing 4 to 10 carbon atoms,inclusive.

4. A heat-sensitive diazoty-pe material comprising a base sheet coatedwith a diazo compound, a coupling component and an alkaline donor zincdialkyldithi-ocarb-amatecyclohexylamine complex, wherein the alkylradicals contain 1 to 5 carbon atoms, inclusive.

5. A heat-sensitive diazotype material comprising a base sheet coatedwith a diazo compound, a coupling component and an alkaline donor zincdimethyldithocarbamate-cyclohexylamine complex.

References Cited by the Examiner UNITED STATES PATENTS 2,732,299 1/1956Morrison 11736.-8 2,967,784 1/1961 Newman et al. 11736.8 2,995,4658/1961 Richey 11736.8 2,999,035 9/1961 Sahler 11736.8 3,057,895 10/1962Marblehead et al. 260-4299 3,076,707 2/ 1963 Lawton et al. 11736.83,149,990 9/1964 Coles et al. 11736.8 3,157,526 11/1964 Johnson et al.11736.8 3,177,233 4/1965 Calhoun 260--429.9 3,185,585 5/1965 Baumann etal 11736.8 3,191,030 6/1965 Huett et. al. 117-36.8

OTHER REFERENCES Kosar: Thermal Development of Diazotype Papers,Photographic Science and Enginering, vol. 5, No. 4, July-August 1961,pp. 239-243.

MURRAY KATZ, Primary Examiner.

1. A HEAT-SENSITIVE DIAZOTYPE MATERIAL COMPRISING A BASE SHEET COATEDWITH A DIAZO COMPOUND, A COUPLING COMPONENT AND AN ALKALINE DONORMETALLIC DIALKYLDITHIOCARBAMATE-AMINE COMPLEX, WHEREIN THE METAL ISSELECTED FROM THE GROUP CONSISTING OF ZINC, CADMIUM AND TELLURIUM, THEALKYL RADICALS CONTAIN 1 TO 5 CARBON ATOMS, INCLUSIVE AND THE AMINE ISSELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AND ALICYCLICAMINESCONTAINING 4 TO 10 CARBON ATOMS, INCLUSIVE.